Low temperature magnetization of the quantum critical heavy fermion superconductor β-YbAlB4

β-YbAlB4 is the first Yb-based heavy fermion superconductor with Tc = 80 mK. We measured low temperature magnetization of high-purity single crystals down to T = 25 mK. The measurements have revealed a considerable amount of volume fractions of the superconductivity and the upper critical field Bc2 curve under field along the c axis, consistent with the previous results. In the normal state, the previously observed divergent behavior in the temperature dependence of the magnetization has been confirmed using higher quality samples and under a low field of 22 mT. In addition, the measurements have revealed a power law behavior, namely, dM/dT ∝ T , which has a slightly higher exponent than the previous results.